SEOUL, South Korea (AP) — South Korea’s president is urging rival North Korea to use the transition of leadership after Kim Jong Il’s death to usher in a new era of peace on the tense Korean peninsula, even as he warned the North against any provocations.

President Lee Myung-bak reached out in his New Year’s message Monday to the North Korean government now led by Kim’s son, Kim Jong Un, saying he has high hopes for a breakthrough this year in negotiations over the North’s nuclear program.

However, Lee warned that Seoul would respond sternly to any North Korean provocations. Relations between the rival Koreas dropped to their lowest point in decades following the 2010 sinking of a South Korean warship that killed 46 sailors and North Korea’s deadly shelling of a front-line island later that year.

Lee’s comments in a nationally televised speech came a day after the North called on its citizens to rally around Kim Jong Un and transform themselves into his “human shields.”

Lee said Kim Jong Il’s death is “portending a sea change” for the fractured Korean peninsula.

“If North Korea comes forward with a sincere attitude, it will be possible for us to work together to open a new era,” he said.

The Korean peninsula remains in a technical state of conflict because the 1950-53 Korean War ended in a truce, not a peace treaty. The Koreas remain divided by a heavily fortified border, and their navies have traded deadly fire at their disputed maritime border over the years.

After a decade of warming ties, relations plummeted in 2008 after Lee took office with a firm policy of linking aid to the impoverished North to its commitment to dismantle its nuclear program. Most joint business ventures and other civilian, humanitarian and cultural exchanges were suspended.

Lee said the Korean peninsula is at a turning point with Kim’s death, and “new opportunities always emerge amid such changes.”

Lee’s speech shows South Korea “has no intention” of provoking North Korea, said Cheon Seong-whun, an analyst with the Korea Institute for National Unification in Seoul.

On Monday, North Korean state media accused Lee of plotting to shake up the North by temporarily placing his troops on high alert after Kim Jong Il’s death. The North’s Rodong Sinmun newspaper said in an editorial that Lee must “kneel down and apologize” for his acts.

However, in one of his first roles as North Korea’s leader, the young Kim met briefly in Pyongyang last week with a former South Korean first lady who was leading private mourning delegations paying respects to Kim Jong Il — a clear sign he is open to reaching out again to the South Koreans.

North Korea’s New Year’s message Sunday didn’t include the country’s routine harsh criticism of the United States and avoided mention of the country’s nuclear ambitions, a sign the North may be willing to continue talks with Washington to win food aid in exchange for denuclearization.

North Korea also repeated a call in the message for implementing past agreements for the Koreas to cooperate on potentially lucrative economic projects.

Lee said negotiations can resume if North Korea halts its nuclear activities.

North Korea, which has tested two atomic devices since 2006, said it wants to return to long-stalled six-nation talks on halting its nuclear weapons program in return for aid. Washington and Seoul, however, have insisted that the North first show progress on past disarmament commitments.

“We are ready to resolve security concerns on the Korean peninsula and provide assistance to revive North Korea’s economy through agreements in the six-nation talks,” Lee said.

The disarmament talks involve the two Koreas, the United States, China, Russia and Japan.

However, Lee vowed that South Korea would maintain a “watertight defense posture” to deal with any North Korean provocations.

“If any aggression occurs, we will respond with strength,” he said.

Meanwhile, North Korea’s propaganda efforts to build up Kim Jong Un continued Monday, with state TV showing him dressed in a dark overcoat and laughing with officers as soldiers applauded during a field inspection. State TV also played a song widely associated with Kim Jong Un: “Footsteps,” a reference to his role carrying out his family’s legacy.

In a city in northeastern North Korea, a large crowd packed a public square and roared as party officials gave speeches praising Kim Jong Il and pledging loyalty to Kim Jong Un, state TV showed. Huge portraits of Kim Il Sung, the country’s founder, and Kim Jong Il and red propaganda signboards stood out from the crowd.

This year is a crucial one for North Korea as it aims to build a “great, prosperous and powerful nation” befitting the April 2012 centenary of the birth of Kim Il Sung, the new leader’s grandfather.